My invention relates to the art of interior lighting and, more particularly, to a novel lighting device wherein light rays propagating through optical wave guides are used as a light source.
My invention may be advantageously used for lighting the interior of human occupancies, such as rooms of a building, underground bomb shelters, underwater enclosures, and so on, with the natural solar beams or rays collected on the earth's surface.
Hitherto, various attempts have been made for utilization of the solar energy reaching upon the earth's surface. However, most of the prior art solar energy systems involve the transformation of the captured solar energy into electric or thermal energy and as far as I am aware there are very few that directly utilize the solar beams themselves as a source of optical energy. In lighting applications, it is obvious that the use of the solar energy in the form of optical energy is advantageous since transformation loss is obviated.
With a view to provide a solar system which employs the solar radiation as a light source, I have previously developed an apparatus for collecting the solar beams capable of condensing the solar beams so that they are introduced into a bundle of optical wave guides (Japanese Patent Laid-Open Publication No. 55-28055). Being reflected at the boundary surface of the optical wave guide, the light rays or solar beams propagate therealong and then issue out of the optical wave guide from its exit end. The angle of emission of the light rays as issuing from the exit end of the wave guide depends on the critical angle of incidence of the material forming the optical wave guide and, normally, is not greater than 48.degree. for an optical fiber made from pure silicate. When the interior of a room is illuminated with light rays issuing from a bundle of optical wave guides, illumination takes place in a spotlight-like fashion. Thus, it is not possible to illuminate a sufficiently wide area with soft light rays.